During the Civil War, or time in US history thereabouts the end of the 19th Century, into the Indian Wars west of the Mississippi, would it be common practice for a member of a group of soldiers to officially keep a detailed log book or journal, basically documentation describing the group's actions? If so, what was the official name for these logs? What type of soldier had this responsibility? And would there be a certain number per a particular unit, e.g. squad, division battalion, brigade, etc.?
While it was common for both officers and men to keep diaries which included their units' daily activities, and for officers to write official accounts of their unit's activities in battles, there was no mandate for official unit "War Diaries" in either the USA or CSA armies. The entire concept was first formalized by the Prussians in 1850, then the British in the aftermath of the Boer War (1908 or thereabouts), and it eventually made its way into the US. War diaries were meant to keep official records of all activities a unit undertook during the war for analysis later, as well as a resource for future historians. However the US army wasn't fighting the types of wars which make such things truly useful prior to the Civil War. The army was small enough that the usual "cultural osmosis" was enough for things to percolate through the whole force. When the Civil War broke out it was always going to be a "short war" that would be "over by Christmas." Though this is speculation on my part, I'd guess that the ad-hoc way troops were assembled and the fact that the US was fairly isolationist weighed against official diaries. When you have to teach your colonel how to order a regiment from column to line, and don't expect to field an army so large ever again, you don't worry about how to document "lessons learned" for next time! With any luck there won't BE a next time! Plus how much are you going to learn from amateurs leading amateurs anyway? (A great deal would be my actual bet, but I can see the argument being made.)
The first true official US war diaries spring up during WWI, and are a staple of WWII and later US conflicts. Generally speaking War Diaries are mandated for each battalion, ship, or squadron, with higher longstanding formations (at least for the US Army, I don't know as much about the USAF/USN/USMC traditions on the subject) keeping their own diary. (So you can have a battalion diary, a divisional diary, etc.)